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Presence of iron is a major factor involved in the degradation of wood from Vasa. As one of different measures to slow down degradation, we are investigating removal of iron and retreatment of wooden objects. Currently a number of loading equipment objects are in treatment, and have reached the final step in the long process of iron extraction, PEG impregnation and finally: drying.

The gentle drying technique of vacuum freeze-drying is used. This technique of drying archaeological waterlogged wood was developed in the 1970's, when the majority of wooden objects from Vasa were already treated and air-dried. The surface tension of liquid water is strong enough to collapse weakened cell structures in waterlogged wood as it evaporates during drying. When freeze-drying under vacuum, the liquid phase of water is avoided as water is transformed directly from its solid phase - ice - to its gas phase - vapour. In this way the wood is gently dried, while the consolidant PEG remains to support its internal structure.

Having no freeze-drying equipment of our own, we turn to our colleagues at Studio Västsvensk Konsevering (external website) in Gothenburg, who run one of the largest vacuum freeze-driers in Sweden. Temperature and pressure are controlled and monitored throughout the process, and the weight stabilisation of the objects tells us when drying is complete.

The objects are placed in the chamber and initially freezed at - 28 C in order to transfer all water to ice. A vacuum pump will then create vacuum, and at such low temperature and pressure drying through sublimation of water occurs. The vapour collects as ice in the condensor at a temperature of about - 47 C.

We estimate that drying will take about three months and hope to see the results of the full retreatment process of the loading equipment objects from Vasa in early summer. Finally!

While I have been writing regularly over the past year specifically about my work with the tools here at Vasamuseet, the tool project is only one of several that I have been involved with during this time. Although I have not written extensively about the others, I have dedicated a significant amount of time to them. Two in particular deserve mention today.

Cannons! Ship sides and hull sections! Replicas! Experimental archaeology! You have likely run across a few of these topics while perusing the blogs here. The ship's side and cannon replica project are two separate research endeavors at the museum that recently concluded and collided (yes, yes, it was intentional) in a particularly spectacular fashion. You may have already seen some news about that, and there will be more descriptive posts forthcoming from the experts. I was not a researcher on either of those projects, but I served as the museum's photographer for internal/technical documentation for both.

It's been refreshing over the past year to take breaks from self-directed research to document and occasionally lend a hand in the development of these other projects. Here are a few highlights in celebration of the recent culmination of both. Not the whole story (you'll get that from the experts) but some of the details you begin to notice and the quieter moments you might catch while observing the evolution of a long-term project. Check back in soon for posts from the project leaders detailing the results.

Guest blogger Ivón Hassel is from Argentina, formed at the University of Kyoto, Associate Professor at the Division of Applied Mechanics of Uppsala University, specialized in timber construction and researcher in the Support Vasa project. Here, Ivón reports in her native language and English on her experimental work on the joints of Vasa:

Dreams can come true

Discover the World!, that was my dream since I was a little child!, and I had no idea that I was going to actually do it!. I use airplanes to go from one place to the other, fast and safe enough, unlike during the 17th century when travelling involved saying goodbye from family and friends, leaving everything behind to an uncertain return. I feel actually very lucky for two reasons, being able to use airplanes instead of Ships (I get easily seasick), and the fact that Ships actually sank, leaving loads of knowledge for us to gain from their remains.

From the north of Argentina, passing through Germany and Israel, I ended up in the most traditional city of Japan, Kyoto. There I spent almost a decade studying, and it became my home. It was while in Japan that I first heard of the Vasa Ship. Just before coming to Sweden for the first time many years ago, a French friend told me: “the only thing you should not miss in Sweden is a visit to the Vasa Museum”. I did not understood why all the fuzz until I entered the museum for the first time and saw her!, she was amazing!

Now I found myself in Sweden again (not that I was lost :P), working at the Division of Applied Mechanics of Uppsala University as an Associate Professor, and as a member of a remarkable group of researchers (I am referring to them! :P)…life is full of surprises and opportunities!.

The goal of the project that I am working on was set very clearly: “Find a way to preserve the Vasa Ship for the coming generations!”. This means finding out how the Ship is deforming in order to being able to design a better support structure for the Ship. Although it is a very ambitious goal, we are a very stubborn and tenacious group of people, and loooove challenges.

My colleagues Ingela Bjurhager, Alexey Vorobyev, and Nico van Dijk have already reached a profound knowledge regarding the properties of the material constituting the Ship. Now, the time has come to zoom out and look at the “research object” at a different scale…

What is the first thing one notice about the Ship? Well… the second…as the first one is her size!. The answer is, her structure, which is a puzzle of many massive pieces of wood put together and working as a whole. From now on I am going to refer to the pieces of wood as “structural members”, and the point at which each of the structural members meet, as “joint”. There are joints throughout the structure of the Ship, and each one of them is a weak point in the structure. Through the joints the loads are transferred from one structural element to the other, and displacement between them is generated. This adds up to the deformation of the ship due to the time-dependent-material deformation, under investigation by my colleagues.

If we want to know how the joints are influencing the overall as well as local deformation of the Ship, the best way (to my opinion) is to perform actual tests on the joints. This means, apply a force and measure the displacement that occurs in different strategic parts of the joint. Due to the difficulties of performing this type of tests directly on the Vasa ship, we decided to do it on a replica of a joint.

Along the way many fantastic people walked with me, sharing their expertise and helping me jump over different obstacles. Fred Hocker, and Anders Ahlgren helped me become acquainted with the Ship’s structure, in order to design the joint to be tested. The best team of carpenters manufactured it, and I must say…I never thought I could have so much fun at work!. Monika Ask, Ove Olssen, Håkan Altrock, Åsa Egerquist and Robert Jonsson made every one of our meetings a memory to keep. The design of the steel testing frame (structure to support the Replica and hold the testing equipment) was designed with the help of hard-working and inquisitive minds, Florian Bommier and Alexey Vorobyev, and the help of Reza Afshar for the computer drawings and modeling. Many nights we stayed at the office with Florian sharing noodles, but very happy doing our job!

Finally the assembly of the Replica in the testing facility of KTH to use their special reinforced floor became a reality!

Different systems were used to measure the displacements on the joint when load was applied. Diferentes sistemas utilizados para la medición de desplazamientos al aplicar cargas.

Two full weeks of applying forces, measuring displacements in different parts of the joint, resulted in an extensive amount of data.

The next step is processing the pool of data, and validating a detailed computer model of the joint. Right after, the material properties of the Vasa-Oak will be included into the verified computer model. Only at this point we are going to have the computer model of the Vasa joint, and we will be ready to quantify the effect of the Vasa joints on the deformation of the Ship.

There is a lot of work for us to do still, so I better go back to it!...I say bye for now until my next post!!!

Mapping! The time has come. As the data stands, I have two binders full of measured drawings and a folder full of high-resolution photographs of the tools, plus pages and pages of notes. These things all deal with the objects as individual things. Now it's time to plug them into the bigger picture and pull the chapter together. Mapping is a really important visualization tool to help us see the relationships between the objects more clearly on a variety of levels.

Right now, the locations in which each object was found exists only as a set of numbers and letters on the individual find records. The eventual goal is to place all of our objects into a 3-D model of the ship so that we can virtually reconstruct what the archaeologists encountered, but all at once and free of mud and water. Pretty exciting possibilities and a hundred years worth of dissertations right there. But in the meantime, we're approaching mapping in a slightly more analog way.

I will take these profiles, traced directly from excavation photographs where we have them and from drawings where we don't, and start plotting them on the plans we have for each of the decks. It will be a visual database made up of multiple layers so that we have the possibility to see different relationhips - for example, the distribution of all the tools that also have bomärke carved into them, alongside tools with decorative marks aside from or in addition to bomärke. Or, all the measuring tools at once. Or all the cutting tools. Or, the knives and awls - things generally thought to be personal equipment, things carried by people in pockets or personal containers - alongside all the human remains. It will help us to visualize how things were distributed at the time Vasa sank, which will contribute to our understanding of what exactly was going on onboard when Vasa set sail on her first and last voyage.